1. Field of the Invention
The present invention relates to a method, a computer program and a device for controlling and/or regulating an electric drive in hybrid vehicles, in particular for entry-level hybridizations having voltages below 60V.
2. Description of the Related Art
In the context of public discussions relating to CO2, and of constantly increasing fuel prices, the importance of systems for reducing fuel consumption and CO2 emissions is increasing. A hybridization of the drive train will therefore increasingly gain in importance.
A goal of hybrid vehicles is the recuperation of the kinetic energy released during braking, or of the potential energy released when traveling downhill. This energy can be used for example to supply the vehicle electrical network, which has a significant influence on fuel consumption.
If the electric motor also enables motoric operation, through an inverter, then the drive moment of the internal combustion engine can be increased (boosted) through an electrical torque, in order for example to increase drivability. If, in addition, e.g. through recuperation, more energy is recuperated than is required for the supplying of the vehicle electrical network and the boost function, there is in addition the possibility of reducing, in a targeted manner, the drive torque of the internal combustion engine, and compensating this through an electrical torque.
Through this shift of load point, a further reduction of fuel consumption can be achieved. Thus, for the hybridization of the drive train a suitable electric motor and a suitable energy storage device, such as for example a lithium-ion battery as power battery, are required, as is a suitable regulation strategy.
In hybrid vehicles, the electric drive can be used either in motoric fashion to support the internal combustion engine or as a generator, e.g. for the recuperation of braking energy. However, if the power battery has a low state of charge, or in general a poor state, e.g. due to temperature or aging, it may be necessary to use generator operation outside of braking phases as well. In this case, the electric drive is not driven from the kinetic or potential energy of the vehicle, but rather must be driven by the internal combustion engine using additional fuel to produce current to charge the power battery or to supply the vehicle electrical network. In this case, generator operation causes an increase in fuel consumption.
For the regulation of the operating modes of the electric drive, i.e. both motoric power and generator power modes, various energy management strategies are possible. The goal of these strategies can be to enforce a target state of charge. This has the result that after a recuperation phase, and thus at a state of charge greater than the target state of charge, a boost phase is introduced until the target state of charge has been reached. However, if the driver requests electrical support over a longer period of time, it is also sought, after this boost phase, to use generator operation of the electric drive to restore the target state of charge as quickly as possible, in this case using fuel to drive the electric drive in generator mode. The goal of restoring the target state of charge as quickly as possible causes cyclization and thus aging of the power battery.
From published German patent application document DE 103 46 213 A1, a method is known for regulating the state of charge of an energy storage device in a vehicle having hybrid drive, in which the state of charge of the energy storage device is regulated by a charge regulating device as a function of the travel speed of the vehicle.